1. Field of the Invention
The present invention relates to a shape memory alloy actuator which includes a shape memory alloy wire portion which contracts by heating by applying current and elongates by cooling, which results in a change in a length thereof.
2. Description of the Related Art
A shape memory alloy actuator which includes a shape memory alloy has hitherto been used. In the shape memory alloy, there exists a state of an austenitic phase and a martensitic phase, and the state changes to the martensitic phase when a temperature is low and to the austenitic phase when the temperature is high. Moreover, at the time of transition (reverse transformation) from the martensite to the austenite, a large distortion restoring force is generated with a small temperature difference. The shape memory alloy actuator is an actuator in which the distortion restoring force is used.
An actuator in which a change in a shape of the shape memory alloy is used has superior characteristics for small-sizing and making light-weight.
For instance, in Japanese Patent Application Publication after examination No. Hei 5-87677, a conventional shape memory alloy actuator has been disclosed. FIG. 7 is a partial cross-sectional front view of a conventional shape memory alloy actuator 101. The shape memory alloy actuator 101 has a structure in which, one end of a wire material of a shape memory alloy 12 is let to be a fixed end 12a and the other end of thereof is let to be a movable end 12b. The movable end 12b moves due to a stress by a bias spring 21 and a force of contraction which is generated when a change in a length of the wire material of the shape memory alloy 12 has changed due to a temperature change by heating by applying current to the wire material of the shape memory alloy 12. Moreover, by covering the wire material of the shape memory alloy toward the fixed end 12a, by a tube member 11 which is insulating and bendable, or flexible, a space reduction of the space memory alloy actuator 101 is also possible.
The space memory alloy actuator 101 controls an amount of distortion by the temperature change in the shape memory alloy 12 by heating by applying current. As a method of control, methods such as controlling an amount of heating by applying current by feeding back a resistance value of the shape memory alloy actuator 12, are available.